The present invention relates to an interlayer placed on cracked pavement. More specifically, this interlayer includes a mixture of aggregate and preferably polymer modified asphalt that is used to delay or minimize the occurrence of cracking, control crack severity, reduce overlay thickness, and enhance waterproofing capabilities.
When pavements deteriorate, they may be overlaid with hot mix asphalt (HMA) to repair them. When designing an overlay, the rate of crack propagation through the overlay, the rate of deterioration of the reflective crack, and the amount of water that can infiltrate through the cracks must be considered. One disadvantage with such HMA overlays is that cracks in the old pavement reflect through the new overlay. To relieve this reflective cracking, thicker overlays are often placed. Another disadvantage with such HMA overlays is that they are permeable allowing water to enter the base. A third disadvantage with these overlays is that they typically have a low strain tolerance and a low resistance to reflective cracking.
Other reflective crack control measures that are used to rehabilitate distressed pavements include placing stress-absorbing membrane interlayers (SAMI), placing grids or fabrics as an interlayer before placing HMA, breaking and seating of pavement, rubblization of pavement, and reconstruction. One disadvantage with some of these processes is that they can be expensive. Another disadvantage with these processes is that if the paved surface is not reconstructed, it may still have cracking problems soon after construction.
As discussed above, one disadvantage with typical HMA overlays is that they have a low resistance to reflective cracking. A typical highway HMA surface mixture has a fatigue life of only about 2000-10,000 cycles, when tested at 10° C. with a strain amplitude of 2000 microstrains and frequency of 10 Hz using a 4-point bending beam apparatus. Accordingly, fatigue resistant interlayers have been introduced to retard reflective cracking. These interlayers may have a fatigue life greater than 200,000 cycles, at identical testing conditions. However, in order to get such a fatigue life and retard the progression of reflective cracks in the pavement, these interlayers sacrifice a degree of its load bearing capacity, as measured in the Hveem stabilometer, and typically have Hveem stabilities of about 18-21.
As a consequence of their high compliance, one disadvantage with these interlayers is that they tend to have inferior load bearing capacity and have a propensity toward showing a lack of dimensional stability under load. In order to compensate for their inferior stability, these interlayers are placed below the top layers of a pavement structure so that they are not exposed to direct traffic loads. Thicker top layers help to improve the total structural stability but are costly. Still further, the top layers of the pavement structure cannot completely compensate for the inferior load bearing capacity of the interlayer.
In order to overcome these disadvantages, an improved interlayer that is able to slow reflective cracking, resist rutting and protect the pavement structure is needed. Still further, this interlayer should be easy to apply and provide a smooth riding surface.